Stop motions for looms

ABSTRACT

A loom stop motion to prevent damage to the warp threads or parts of the loom if the shuttle is incorrectly picked, employs a detector 28 midway along the sley a detector 36 associated with the loom crankshaft. The detector 38 signals the passage of the shuttle and the detector 36 signals a time in the loom cycle. A simple logic circuit is provided, and the pulses from the two detectors are fed into a bistable system A and then to comparators B and C. The pulses from the comparators are fed into a pulse lengthener D, an output amplifier E and into a relay F, the relay F, in turn, controlling a solenoid 162. The solenoid 162 trips the loom stop mechanism and causes the loom to stop. The invention works on the assumption that if the speed of travel of the shuttle is correct, then it will become properly housed in the receiving shuttle box.

United States Patent [72] Invento Davi Ainsworth 3,373,773 3/1968Balentine, Jr. et al. 1. 139/1 Darwen; 3,439,716 4/1969 Adams 139/336Cyril Millward Atkinson, Carniorth, both 3,451,438 6/1969 Wilde et a1139/341 X England FOREIGN PATENTS [21] P 22 1,541,187 8/1968 France139/341 [22] 158,837 1 1963 U.S.S.R. 139/341 Patented Oct. 19, 1971 [73]Assignee Northrop Weaving Machinery Limited OTHER REFERENCES Daisyfield,Blackburn, England Electronic Protection for Looms" by Victor Sepavich,[32] Priority Mar. 2, 1968 received by US Patent Office May 9, 1950,copy in GR. 364 zg Primary Examiner-James Kee Chi Attorney-Norris &Bateman [54] STOP MOTIONS FOR LOOMS 18 Claims 10 Drawmg Figs ABSTRACT: Aloom stop motion to prevent damage to the [52] US. Cl 139/336, warpthreads or parts of the loom if the shuttle is incorrectly DQ3d51/44picked, employs a detector 28 midway along the sley a detec- [51] int. MD l3d5l/Q 2 tor 36 associated with the loom crankshaft, The det ctor 38Field of Search ..139/341,336, 1 signals the passage of the shuttle andthe detector 36 signals a time in the loom cycle. A simple logic circuitis provided, and the pulses from the References cued two detectors arefed into a bistable system A and then to UNITED STATES PATENTScomparators B and C. The pulses from the comparators are 2,567,751 91951 \Volke 139 341 fed into a Pulse lengthener D, an Output amplifier Eand into 2,586,335 2 1952 Howe,.lr. et a1. 139 341 relay F, the relay F,in mm, controlling a Solenoid The 2 753 894 7 195 Lovshin 6 3L 139 1solenoid 162 trips the loom stop mechanism and causes the 2 339 1959Turner 39 33 loom to stop. The invention works on the assumption that if3,047,030 7/1962 Metzler 139/336 he speed of travel of the shuttle iscorrect, then it will become 3,181,573 5/1965 Stutz 139 341 P p y housedin the receiving shuttle PATENTEDUBT 19 I9?! 3.613.742

sum 10F 9 INVENTORB DAVID AINSWORTH & CYRIL MILkWARD BY TKIN-SONPATENTEUUCT 19 Ian MP EH INVENTORB DAV ID AINSWORTH & CYR IL MILLWARDATKINSON PATENTEDUET l9 |97l SHEET H [1F 9 INVENTORS DAVID AINSWORTH &CYRIL MILLWARD ATKINSON PATENIEUHB 1 3.613.742

sum 5 0F 9 INVENTORB DAVID AINSWOR'IH 6 CYKIL MILLWARI) ATKINSUNPATENTEDUCT 191s?! 3, 13,742

SHEET 80F 9 INVENTORS DAVID AINSWORTH & CYRIL MILLWARD ATKI SON BY(UOMM) mum PATENTEDUCT 19 I9?! SHEET 7 [1F 9 PAIENIEnw 19 3,613,742

"SHEET 90F 9 i o us 5 o o l Q Y INVENTOR8 DAVID AINSWORTH & CYRILMILLWARD ATKINSON BY MOMMA, Mm

STOP MOTIONS FOR LOOMS A simple logic circuit is provided, and thepulses from the two detectors of fed into a bistable system A and thento comparators B and C. The pulses from the comparators are fed into apulse lengthener D an output amplifier E and into a relay F, the relayF, in turn, controlling a solenoid 162. The solenoid 162 trips the loomstop mechanism and causes the loom to stop. The invention works on theassumption that if the speed of travel of the shuttle is correct, thenit will become properly housed in the receiving shuttle box.

During the operation of a loom, it is necessary to stop the loom veryquickly if the shuttle which has been picked does not arrive in theshuttle box towards which it has been propelled at the correct time.This is because if the reed beats up with the shuttle still in the shedof warp threads there will be widespread damage to the warp threadsthemselves, and possibly furtherdamage to the reed and/or the shuttle.

The conventional stop motion employs a pivoted dagger" below the shuttlebox, and lifted by engagement of the shuttle with a swell in the wall ofthe box, so that it does not engage with a spring-loaded frog on thebreastbeam of the loom. If the shuttle does not arrive in correct time,then the dagger is not lifted and consequently it strikes the frog" asthe sley moves forward for the beat-up. This turns the frog against itsspring loading and the turning of the frog causes the starting handle tomove to the ofl position, thus disconnecting the drive to the loomcrankshaft and applying the brake. In practice, however, there is such ashort time between the detection of the nonarrival of the shuttle andthe arrival of the sley at front and the center, that the brake does nothave time to arrest the sley, frog acts as a baulking member, so that alarge part of the kinetic energy of the sley is absorbed by thespringloading of the frog. This places severe strains on the frog dagger, sleyand breast beam of the loom and these parts have to be designed towithstand such strains.

Obviously the main problem is that created by the very short timeinterval between the detection and the position at which damage wouldoccur. If the shuttle is not detected until it arrives in the shuttlebox at the opposite side of the loom to that from which it was pickedthere is, only about of crankshaft movement in which to stop the loom toavoid damage to the warp and reed.

The principal object of this invention is to provide a stop motion for aloom, which will allow a greater part of the loom cycle between faultypicking detection and the point at which the loom must be stopped sothat application of the brake is more effective and therefore stressesapplied to parts of the loom are reduced.

According to this invention a loom stop motion comprises means fordetecting the passage of a shuttle at some position intermediate theshuttle boxes at opposite ends of the sley, comparator means forcomparing the time of the shuttle passing the detection position withthe loom cycle and control means operative if the comparator signalsincorrect timing to arrest the sley.

Stated in another way, the inventive concept of that of detecting theshuttle speed during its flight and using this detected speed toindicate correct or incorrect picking to control the continuation of themovement of the sley. This is a basically different approach to theproblem than that of the conventional swell-frog-dagger arrangementwhich only detects the arrival of the shuttle. The invention works onthe assumption that if the speed of travel of the shuttle is correct,then it will become properly housed in the receiving shuttle box. It isconceivable that this might not always prove correct, but the chances ofincorrect picking if the shuttle travels at the correct speed areremote, since nearly all picking faults originate at the starting end ofthe shuttle flight.

A loom stop motion, in accordance with the invention will now bedescribed by way of example only, with difference to the accompanyingdrawings, in which:

FIG. I is a diagrammatic representation of the shuttle path of a loom,

FIG. 2 is a collar on the crankshaft of a loom,

FIG. 3 is a block diagram ofa control circuit for a loom,

FIG. 4 is an electronic control circuit,

FIG. 5 is a graphical representation of the timing,

FIG. 6 is a perspective view of part of a stop mechanism for a loom, I

FIG. 7 is a front view of a stop mechanism as shown in Figure 6,

FIG. 8 is an end view of a stop mechanism as shown in Figure 6,

FIG. 9 is a view of a starting handle for the mechanism, and

FIG. 10 is a representation of a mechanical clutch and brake assembly,

For simplicity of description, it is assumed that there is only a singleshuttle box at each end of the sley, although it will be understood thatthe invention is equally applicable to more complicated shuttle boxarrangements.

Referring to FIG. 1 there is shown a loom sley 20 with its shuttle boxes21 and 23 and a race board 22. A shuttle 24 is illustrated in theshuttle box 23. When the loom is in operation, the shuttle is picked toand fro across the sley and at the same time the sley oscillatesforwards and backwards to beat up the weft.

Two magnetic pickups are fitted to the loom to provide detection of theshuttle flight and comparison with the loom cycle. One of these-ashuttle detector 28 is fitted into the sley 20 with its top flush withthe race board 22, and the shuttle 24 for use in the loom is fitted witha magnet 26 to operate the pickup 28. In this particular arrangement (asshown in FIG. I), a small permanent magnet disc 26 is fitted into thebase of each shuttle 24, so that the shuttle is exactly at the midpointin its flight when its magnet 26 is over the pickup 28. This conditionwill apply in both direction of shuttle flight.

A second pickup 36-the crankshaft pickup-is fixed to a stationary partof the loom frame, close to the loom crankshaft 32. A collar 30 isfitted on to the crankshaft 32 (as shown in FIG. 2) at this position anda magnet 34 projects radially from the collar 30. The disposition of thecrankshaft pickup 36 provides that it is energized by the magnet 34 onthe collar 30 once in each revolution of the crankshaft 32, and thecollar can be adjusted about the crankshaft axis, so that the timing ofthe crankshaft pickup operation, relatively to the loom cycle, can bepreset.

For the purpose of utilizing the signals received from the two pickups29 and 36, an electrical control box is provided on the loom and thisincorporates a transistorized circuit, which is shown in FIGS. 3 and 4.

The control circuit comprises a bistable system A, comparators B and C,a pulse-lengthening circuit D an output amplifier E and a control relayF (as shown in FIG. 3). A more detailed diagram of the control circuitis shown in FIG. 4 and has a seven-transistor circuit. The transistorsare combined with resistors, capacitors and diodes forming a simplelogic and amplification circuit.

The input to each comparator B and C from the bistable system A, whenthe pulse arrives at the comparator, must be the same as it was beforethat pulse changed the bistable system over. This can be achieved, forexample, by introducing a delay between the bistable system and thecomparator. In the circuit shown in FIG. 4, the delay is provided bydiode sinking circuits 50 and 52.

The signals from the comparators are fed into the pulselengtheningcircuit D, and the lengthened output signal from this circuit isamplified by the amplification circuit E and this signal then causesdeenergization of the relay F which is energized whilst the loom isrunning.

The principle of operation is that when the loom is running normally,the pulse from the shuttle pickup 28 occurs before the pulse from thecrankshaft pickup 36 in each picking cycle. In a succession of pickingcycles, therefore, shuttle and crankshaft pulses alternate, and thecontrol is designed to allow the loom to run only so long as thissequence is maintained.

If, in a particular picking cycle, the shuttle 24 arrives late at thedetection position the corresponding crankshaft pulse will precede theshuttle pulse; the effect of this will be that the crankshaft pulse ofthe previous picking cycle will be followed by another crankshaft pulse,the alternating sequence will be broken and the control system willcause the Ioorn to stop.

If for some reason (such as the collar 30 carrying the magnet 34becoming loose on the crankshaft 32) the crankshaft pulse failed, thesequence will also be broken, because the shuttle pulses will not thenalternate with crankshaft pulses, and the loom will be stopped.

In FIG. 3 the block A represents a bistable system which is set by theshuttle pulse and reset" by the crankshaft pulse. The comparators, shownby blocks B and C, compare the outputs of the bistable system with theincoming pulses, and as previously mentioned the system is so arrangedthat this comparison takes place before the bistable system is switchedover. A signal only appears at the output of either comparator, if theincoming signal is such that its effect would be to switch the bistableto the condition which already exists. For example when a crankshaftpulse appears at the input, the effect is normally to reset the system.If it is already in the reset condition, then a signal will appear atthe output of comparator B. The system shown by the blocks D and Ecauses the loom to be stopped in response to a signal at the output ofeither comparator, also acts as an amplifier for the output signal. Thissignal is applied to the normally open relay F, and it will be notedthat when the loom is running, the relay will be energized. In this wayit will be seen that the output of the bistable system defines whichpulse is expected" next (i.e. shuttle or crankshaft, and the arrangementprovides that if the last pulse was a shuttle pulse, the next must be acrankshaft pulse and vice versa.

This satisfies the conditions required for detecting late shuttle picks,or other faults as outlined previously.

Typical conditions are shown in FIG. 5, in which the lefthand part ofthe diagram shows three shuttle pulses SP and three crankshaft pulses,CP, whilst the line marked shows the signal obtained at the output ofthe circuit (i.e. at the output of block E in FIG. 3).

Beginning at the left, there is shown the normal condition obtained whenthe shuttle crosses the shuttle pickup at the correct time in the loomcycle indicating that it has adequate velocity to arrive correctly inthe shuttle box at the receiving end of the loom. The shuttle pulse 40is before the crankshaft pulse 41 so that the output is maintainedthroughout the cycle. This means that the relay remains energized, andthe loom continues to run.

In the second cycle, the limiting condition is shown where the shuttlesignal 42 is only just before the crankshaft signal 43 indicating thatalthough the picking is not quite correct, the shuttle should haveenough velocity to arrive safely. Again, there is the full output signaland the relay remains energized.

In the third cycle, the shuttle arrives late at the detection positionand the crankshaft pulse 45 precedes the shuttle pulse 44 indicatingthat the shuttle will not arrive correctly before the beat-up. Thisproduces a zero output indicated at Ov in FIG. 5 which will cause theloom to be arrested. When the loom has stopped the control system resetsautomatically so that the loom may be restarted.

The relay F is arranged to control a solenoid 162 (see FIG. 6) whichforms part of a mechanical system for controlling the driving of theloom. So long as the solenoid 162 remains energized, the loom continuesto run, but as soon as the solenoid is deenergized the loom is arrested.

In the right-hand part of FIG. 5, there are illustrated the variouspulses and signals which occur if for some reason, the crankshaft pulsewere to fail. In this event, there would be two shuttle pulses 46 and 47without a crankshaft pulse between them, and therefore the secondshuttle pulse 47 would produce a zero output signal, which releases therelay F and stops the loom.

The electronic circuit provides a simple logic circuit which willmaintain a constant energization of the relay F so long as the twopickups pulse alternately. As soon as there occurs two successive pulsesof either pickup without an intervening pulse from the other, thecircuit signals a fault and the loom is stopped.

Taking 0 in the loom cycle as being the position when the cranked partsof the loom crankshaft are vertically above the axis of the crankshaft,the shuttle should arrive at the midpoint in its flight at about 265 andit should be possible to set the crankshaft pickup 36 to operateimmediately after this. The brake then has approximately 1 10 of theloom cycle in which to operate before damage would occur. This is alarge increase on the approximately 12 of movement available forstopping the loom with the conventional arrangement.

The output from the detection system described with reference to FIGS. 1to 5, is applied to mechanical means, controlling the operation of theloom, as shown in FIGS. 6 to 10. Referring firstly to FIG. 10, their isshown a combined clutch/brake unit 100 which forms part of theIoom'driving mechanism.

The loom-driving motor is shown at 102, and there is a belt drive 104 toa pulley 106 free to rotate on a shaft 108, which drives the loom. Thepulley 106 also acts as the driving member of the clutch. The shaft 108is joumaled in a stationary member 110 on the loom frame, and thismember 110 also acts as a brake.

Between the member 110 and the pulley 106, there are two driven members112 and 114 each of which is mounted on a splined part of the shaft 108,so that these members rotate with the shaft. The driven members 112 and114 are identical, but are mounted back to back as shown. Each has atoggle lever system 118 and the driven members are loaded by springs 120or 122 towards the brake member 110 and the pulley 106 respectively. Afriction lining 116 is provided on the outer face of each driven member.

Between the driven members there is a thrust member 124 pivoted at 126and engaged between thrust blocks 128 and 130 slidable on the shaft 108.When the thrust member 124 pushes the block 128 to the left, the togglemechanism is operated to pull the driven member 112 out of engagementwith the brake member 110. Similarly, when the thrust member is moved tothe right, the driven member 114 is pulled out of engagement with thepulley 106.

In the next position, the sets of springs and 122 push their respectivedriven members 112 and 114 into engagement with the brake 110 and pulley106 respectively, but the spring loading is such that the brake isoperative and the clutch slips so that the shaft 108 is not driven andthe loom is at rest.

A clutch connecting rod 184 is connected to the thrust member 124 sothat axial movement of the rod causes operation of the thrust member.

Turning now to FIGS. 6, 7 and 9, there is illustrated a settingmechanism which is used to put the clutch into engagement so that drivecan be transmitted from the loom-driving motor 102 to the loomcrankshaft. The loom has a starting handle carried by a member 132 whichhas an arm 136. The member 132 is pivoted at 138 on the side frame ofthe loom, and a light tension spring 137 connected between the arm 136and the side frame, normally pulls the member 132 into the positionshown in FIG. 9, where is engages with an adjustable screw stop 140.This if the off position of the starting handle, and corresponds to theposition when the loom is at rest. A boss 133 projects from the member132 and overlies a lever 134 7 also pivoted at 138, and a connecting rod142 is pivoted at one end on the lever 134 and at its other end, ispivoted on the depending arm 144 ofa bellcranked operating lever 146pivoted at 148 on the loom side frame.

When the starting handle 130 is turned about the pivot 138 in ananticlockwise direction as seen in FIG. 9, it can be brought into aposition, where the member 132 engages with an adjustable screw stop 150fixed on the side frame of the loom, and in doing so, it presses thelever 134 down into the on position of the loom, in which condition, theloom is operative. The chain dotted line 152 in FIG. 9 shows theposition of the longitudinal axis of the connecting rod 142 in the on"position and it will be observed that if any axial pull is applied tothe connecting rod 142 in this position, it exerts a locking turningmoment on the lever 134 because the rod 142 has overcenter of thepivotal axis of that lever. This constitutes an important feature of thesetting mechanism, because it ensures once the lever 134 has been movedto the on" position it cannot be restored to the off position by axialpull applied along the connecting rod 142. The handle 130 will beimmediately restored to its original position by the spring 137 when theoperator releases it, and thereafter it is disconnected from the lever134 so long as the loom is running.

The bellcranked lever 146 has a bifurcated arm 154 to which is pivotallyconnected the upper end of a catch 156. The latter passes verticallythrough a slot 158 in a latch 161 attached to the armature 160 of asolenoid 162. A rod 164 attached to the armature 160 extends out throughthe opposite side of the solenoid 162, through a bracket 166 fixed tothe side frame of the loom and terminates in a head 168. A compressionspring surrounds the portion of the rod 164 between the head 168 and thebracket 166 and this compression spring urges the armature 160 to theleft as seen in FIG. 7, thus tending to pull the catch 156 to the left.

A three-armed operating lever 172 (see also FIG. 8) is pivoted on afixed pin 174, and forms the principal member of an automatic mechanismfor operating the clutch and brake mechanism shown in FIG. 10. Theoperating lever 172 has a short substantially horizontal arm 176, and aboss 178 fixed on this arm 176 is capable of engagement by a shoulder180 formed on the catch 156, when the latter is pushed re the right asseen in FIG. 7 by energization of the solenoid 162. So long however asthe solenoid 162 remains deenergized the spring 170 pulls the armature160 to the left and so pulls the catch 156 into a position where theshoulder 180 is disengaged from the boss 178.

An upwardly extending arm 182 of the operating lever 172 carries at itstop end, the pivotal connection for the connecting rod 184, the otherend of which is connected to the clutch thrust member 124 (see FIG. 10).

A downwardly depending arm 186 of the operating lever 172 is pivoted atits bottom end, to a thrust block 188, the lower end of which isslidable within a cylinder 190 pivoted at 192 on a fixed part of theloom frame. A series of Bellville washers 194 is placed back to backinside the tube 190, in order to provide a powerful compression springacting between a fixed block (not shown) within the tube 190, and thelower end of the thrust block 188. The disposition of the operatinglever 172, and the pivoted tube 190 when the connecting rod 184 holdsthe thrust member 124 in the position where the brake 110 is engaged bythe driven member 112 is shown in full lines in FIG. 8. In thisposition, of course, the starting handle 130 would be in the offposition. However, when the starting handle is moved to the on position,it turns the lever 134, and this exerts a pull through the connectingrod 142, which in turn turns the bellcranked lever 146 about its pivot,depressing catch 156. If the solenoid 162 is energized when the startinghandle is depressed, the latch 161 holds the catch 156 in the positionsuch that the shoulder 180 engages with the boss 178, the operatinglever 172 will be turned by the downward movement of the catch 156, andwillv be brought into the position illustrated in chain dotted lines inFIG. 8. During this movement into the on position the powerful spring194 will be compressed, but once the lever 172 arrives at the positionshown in the chain dotted lines, the spring 194 will act axially alongthe centers of the pivot joining the thrust block 188 to the arm 186 andthe pivot 174, so that it will exert no turning moment on the lever 172.In this position, the connecting rod 184 will have pressed the thrustmember 124 to disconnect the brake and connect the clutch and drive willbe transmitted from the motor 102 to the shaft 108, so that the loomwill be set in motion.

The movement of the driven member 112 into the disengaged position willplace the springs 120 in compression, and at the same time will relaxthe springs 122. Consequently, the springs 120 will be constantlytending to engage the brake.

However, this force will be transmitted back through the connecting rod184, operating lever 1.72, catch 156 (so long as the solenoid 162remains energized) bellcranked lever 146 and connecting rod 142. It willbe recalled, that an axial thrust along the rod 142 only serves to lockthat rod, when the lever 134 is in the on position and therefore theentire setting and automatic mechanism is at this stage irreversible,and consequently the clutch remains engaged.

Supposing now that in this condition the solenoid 162 is deenergized andbecause of the change in the output from the comparators, then thespring 170 will pull the armature 160 and this in turn will disconnectthe catch 156 from the boss 178. The lever 172 is then free to turnabout its pivotal axis 174. As has been mentioned the springs will betending to engage the brake and as soon as they apply a slight turningmoment to the lever 172 (through the connecting rod 184) the spring 194will begin to exert a turning moment on the lever 172, and this willhave the result snapping the lever 172 quickly into its originalposition, at the same time pulling the driven member 112 into thebrake-engaged position. Thus, the arrangement of the pivoted tube 190with its powerful spring 194 can be considered as a servomechanisminitiated by the comparatively light force of the brake springs 120 andthen amplified by the powerful force of the spring 194. The effect is toproduce a very rapid change over from the clutch-engaged position to thebrake-engaged position and this produces the necessary stopping of theloom. The loom is then ready to be restarted by hand, and since thesolenoid 162 has been reenergized almost immediately (as previouslydescribed), it is only necessary for the operative to pull the startinghandle into the on position.

The mechanism shown in FIGS. 6 to 10 can therefore be considered as asetting mechanism which comprises the linkage between the startinghandle 130 and the catch 156 and an automatic operating mechanism whichcomprises the lever 172 with its associated spring mechanism 194 and theconnecting rod 184. The setting mechanism and automatic mechanism arecapable of connection or disconnection by the operation of the solenoid162.

Referring to FIG. 4, a warp stop switch 60 and a manual stop switch 62are connected in the bistable system as shown, and when either of theseis energized, the system is set to expect a crank pulse. Therefore whenthe shuttle passes the detector 28, the relay will be deenergized andthe loom will stop with the shuttle housed in a shuttle box. Thus thesystem is used to stop the loom correctly on a warp breakage or manualoperation of a stop switch.

Further, a reset switch 64 is connected to the bistable system as shown,and this switch is positioned on the loom so that it is closed each timethe lever 134 returns to the original set position. This has the effectof causing the system to expect a shuttle pulse whenever the loom isstarted and this is the necessary condition for starting the loom.

The invention is capable of being carried out in various ways. In theabove example, the logic system is electronic, but it will beappreciated that electrical (relays), pneumatic, fluidic, hydraulic oreven mechanical systems could be employed. Furthermore, the shuttledetector could be positioned at some other point along the sley, butwhilst that would increase the time available in one direction ofshuttle flight, it would lessen it in the other.

This could be overcome by using two shuttle detectors, one near to eachend of the sley, but a more complicated logic system would then berequired. It should also be understood that a magnetic or electricalclutch and/or brake could be employed.

We claim:

1. A loom stop motion for use in a loom having a sley; a shuttle movablebetween shuttle boxes at opposite ends of said sley, and a loom cyclicdrive mechanism, comprising first signal-generating means locatedadjacent the slcy intermediate said shuttle boxes for detecting thepassage of the shuttle between said shuttle boxes; secondsignal-generating means responsive to operation of said cyclic drivemechanism; comparator means for receiving signals from said first andsecond signal-generating means and adapted to maintain a constant outputso long as the first and second signals are received alternately, but tochange its output as soon as two like signals are received insuccession; and control means connected to said comparator means andoperative upon a change in the output signal to arrest the sley.

2. A loom stop motion as claimed in claim 1, in which the comparatormeans includes a bistable electronic circuit, and the first and secondsignal-generating means are adapted to give electrical pulses to thecomparator means, so that the output potential from the comparatorremains constant so long as first and second pulses are receivedalternately, but changes as soon as two like pulses are receivedsuccessively.

3. A loom stop motion as claimed in claim 2, in which the output signalfrom the comparator controls the operation of a solenoid which in turncontrols a clutch and brake mechanism for driving or arresting the loomsley.

4. A loom stop motion as claimed in claim 3, in which means are providedfor amplification of the output signal from the comparator.

5. A loom stop motion as claimed in claim 2, in which the electroniccircuit includes transistors.

6. A loom stop motion as claimed in claim 2, in which said firstsignal-generating means includes a magnetic pickup detector carried bythe sley and adapted to be operated by a magnet carried by the shuttle.

7. A loom stop motion as claimed in claim 2, in which said firstsignal-generating means includes a proximity switch carried by the sleyand adapted to be operated by a magnet carried by the shuttle.

8. A loom stop motion as claimed in claim 6, in which the magneticpickup detector is adapted to be operated when a part of the shuttlepasses a position midway along the length of the sley.

9. A loom stop motion as claimed in claim 2, said loom drive mechanismcomprising a loom crankshaft, said second signalgenerating meanscomprising a magnetic pickup cooperating with a magnet, either thepickup or the magnet being fixed to a part rotatable at the same angularvelocity as the loom crankshaft, and the other being fixed on astationary part of the loom.

10. A loom stop motion as claimed in claim 2, said loom drive mechanismcomprising a loom crankshaft, the second signal-generating meanscomprising a proximity switch cooperating with a magnet, either theswitch or the magnet being fixed to a part rotatable at the same angularvelocity as the loom crankshaft, and the other being fixed on astationary part of the loom.

11. A loom stop motion as claimed in claim 9 in which the rotatable partis a collar adjustably fixed on the loom crankshaft.

12. A loom stop motion as claimed in claim 1, in which the control meanscomprises a setting mechanism capable of' manual operation and anautomatic mechanism capable of holding the loom drive mechanism ineither an operative or inoperative position, and a latch mechanismcapable of coupling the setting mechanism to the automatic mechanism, sothat when so coupled, the setting mechanism can be used to place theloom drive mechanism in the operative condition.

13. A loom stop motion as claimed in claim 12, in which the automaticmechanism is biased towards the loom inoperative condition, and thesetting mechanism includes an overcenter device whereby it prevents theautomatic mechanism putting the loom into the inoperative condition solong as the latch mechanism is engaged,

14. A loom stop motion as claimed in claim 13, in which there is aservomechanism operative in the automatic mechanism whereby once thedrive mechanism begins to change from the operative to the inoperativecondition, the

change is effected with amplified power.

15. A loom stop motion as claimed in claim 14, wherein theservomechanism comprises pivoted means acted upon by spring means and soarranged that the spring means exercises no turning moment so long asthe drive mechanism is in the operative condition, but exercises aturning moment on the pivoted means as soon as the drive mechanismchanges even slightly from the operative condition.

16. A loom stop motion as claimed in claim 15, said latch mechanismincluding a solenoid operated by the output signal from said comparatormeans, and said loom drive mechanism including a clutch and brakemechanism operated by said automatic mechanism.

17. A loom stop motion as claimed in claim 16, in which the solenoid isnormally energized by the output signal from the comparator means tohold the latch mechanism against a resilient loading.

18. A loom stop motion as claimed in claim 14, in which resilient meansare operative on the setting mechanism to return the latter to itsoriginal position when the latch mechanism is released.

1. A loom stop motion for use in a loom having a sley; a shuttle movablebetween shuttle boxes at opposite ends of said sley, and a loom cyclicdrive mechanism, comprising first signal-generating means locatedadjacent the sley intermediate said shuttle boxes for detecting thepassage of the shuttle between said shuttle boxes; secondsignal-generating means responsive to operation of said cyclic drivemechanism; comparator means for receiving signals from said first andsecond signal-generating means and adapted to maintain a constant outputso long as the first and second signals are received alternately, but tochange its output as soon as two like signals are received insuccession; and control means connected to said comparator means andoperative upon a change in the output signal to arrest the sley.
 2. Aloom stop motion as claimed in claim 1, in which the compaRator meansincludes a bistable electronic circuit, and the first and secondsignal-generating means are adapted to give electrical pulses to thecomparator means, so that the output potential from the comparatorremains constant so long as first and second pulses are receivedalternately, but changes as soon as two like pulses are receivedsuccessively.
 3. A loom stop motion as claimed in claim 2, in which theoutput signal from the comparator controls the operation of a solenoidwhich in turn controls a clutch and brake mechanism for driving orarresting the loom sley.
 4. A loom stop motion as claimed in claim 3, inwhich means are provided for amplification of the output signal from thecomparator.
 5. A loom stop motion as claimed in claim 2, in which theelectronic circuit includes transistors.
 6. A loom stop motion asclaimed in claim 2, in which said first signal-generating means includesa magnetic pickup detector carried by the sley and adapted to beoperated by a magnet carried by the shuttle.
 7. A loom stop motion asclaimed in claim 2, in which said first signal-generating means includesa proximity switch carried by the sley and adapted to be operated by amagnet carried by the shuttle.
 8. A loom stop motion as claimed in claim6, in which the magnetic pickup detector is adapted to be operated whena part of the shuttle passes a position midway along the length of thesley.
 9. A loom stop motion as claimed in claim 2, said loom drivemechanism comprising a loom crankshaft, said second signal-generatingmeans comprising a magnetic pickup cooperating with a magnet, either thepickup or the magnet being fixed to a part rotatable at the same angularvelocity as the loom crankshaft, and the other being fixed on astationary part of the loom.
 10. A loom stop motion as claimed in claim2, said loom drive mechanism comprising a loom crankshaft, the secondsignal-generating means comprising a proximity switch cooperating with amagnet, either the switch or the magnet being fixed to a part rotatableat the same angular velocity as the loom crankshaft, and the other beingfixed on a stationary part of the loom.
 11. A loom stop motion asclaimed in claim 9 in which the rotatable part is a collar adjustablyfixed on the loom crankshaft.
 12. A loom stop motion as claimed in claim1, in which the control means comprises a setting mechanism capable ofmanual operation and an automatic mechanism capable of holding the loomdrive mechanism in either an operative or inoperative position, and alatch mechanism capable of coupling the setting mechanism to theautomatic mechanism, so that when so coupled, the setting mechanism canbe used to place the loom drive mechanism in the operative condition.13. A loom stop motion as claimed in claim 12, in which the automaticmechanism is biased towards the loom inoperative condition, and thesetting mechanism includes an overcenter device whereby it prevents theautomatic mechanism putting the loom into the inoperative condition solong as the latch mechanism is engaged.
 14. A loom stop motion asclaimed in claim 13, in which there is a servomechanism operative in theautomatic mechanism whereby once the drive mechanism begins to changefrom the operative to the inoperative condition, the change is effectedwith amplified power.
 15. A loom stop motion as claimed in claim 14,wherein the servomechanism comprises pivoted means acted upon by springmeans and so arranged that the spring means exercises no turning momentso long as the drive mechanism is in the operative condition, butexercises a turning moment on the pivoted means as soon as the drivemechanism changes even slightly from the operative condition.
 16. A loomstop motion as claimed in claim 15, said latch mechanism including asolenoid operated by the output signal from said comparator means, andsaid loom drive mechanism including a clutch and brake mechanismoperated by said automatic mechanism.
 17. A loom stop motion as claimedin clAim 16, in which the solenoid is normally energized by the outputsignal from the comparator means to hold the latch mechanism against aresilient loading.
 18. A loom stop motion as claimed in claim 14, inwhich resilient means are operative on the setting mechanism to returnthe latter to its original position when the latch mechanism isreleased.